|I’d Call It That||3.0||6.06||1||(Andrew)|
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I agree. It’s hard to compare, like you say. It would be neat to see them growing side-by-side. Still, doesn’t necessarily mean there’s a difference. Witness, to wit, the occasional times one sees a brown form of Bacidia schweinitzii growing right next to a black form — still the same species, even though growing very differently in identical conditions.
It’s hard to compare the two visually precisely, since they’re growing on two different types of trees and form slightly different shapes. The one here is pretty obviously oval extended horizontally, but the other one is interrupted by rough bark, and it’s hard to perceive what shape it would take if it were on smooth bark. Identical to this one? Shapes probably don’t feature much in IDs anyway, do they? – since they’re affected by a bunch of factors, including but not limited to the type of bark.
Makes one wonder how good these two species are, if the only difference is the presence of a variable quantity of a single xanthone, doesn’t it??
But worth noting “officially” so that people know this id is accurate! UV test is important for this species. The otherwise similar species O. androgyna (according to Brodo et al. 2001, Lichens of N. Amer.) has thicker thallus and larger, yellower soralia. The primary difference is that O. arborea has lichexanthone in the soralia and sometimes in the thallus, O. androgyna does not. You sent me specimens from this location both with and without lichexanthone.
(Note that lichexanthone is very easy to test for: most over-the-counter UV LED flashlights will cause it to fluoresce very bright yellow. Many UV+ lichen substances require 350 nm, which is expensive and hard to get hold of, but this one shows up just fine even in 375-380 nm.)
Created: 2012-02-14 23:06:35 CST (-0600)
Last modified: 2012-02-14 23:09:10 CST (-0600)
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